1. Field of the Invention
The present invention generally relates to eye gaze trackers and, more particularly, to techniques for improving accuracy degraded by ambient light noise while maintaining safe IR levels output by the illuminator.
2. Description of the Related Art
The purpose of eye gaze trackers, also called eye trackers, is to determine where an individual is looking. The primary use of the technology is as an input device for human-computer interaction. In such a capacity, eye trackers enable the computer to determine where on the computer screen the individual is looking. Since software controls the content of the display, it can correlate eye gaze information with the semantics of the program. This enables many different applications. For example, eye trackers can be used by disabled persons as the primary input device, replacing both the mouse and the keyboard. Eye trackers have been used for various types of research, such as determining how people evaluate and comprehend text and other visually represented information. Eye trackers can also be used to train individuals who must interact with computer screens in certain ways, such as air traffic controllers, nuclear energy plant operators, security personnel, etc.
The most effective and common eye tracking technology exploits the “bright-eye” effect. The bright-eye effect is familiar to most people as the glowing red pupils observed in photographs of people taken with a flash that is mounted near the camera lens. In the case of eye trackers, the eye is illuminated with infrared light, which is not visible to the human eye. An infrared (IR) camera can easily detect the infrared light re-emitted by the retina. It can also detect the even brighter primary reflection of the infrared illuminator off of the front surface of the eye. The relative position of the primary reflection to the large circle caused by the light re-emitted by the retina (the bright-eye effect) can be used to determine the direction of gaze. This information, combined with the relative positions of the camera, the eyes, and the computer display, can be used to compute where on the computer screen the user is looking.
Eye trackers based on the bright-eye effect are highly effective and further improvements in accuracy are unwarranted. This is because the angular errors are presently smaller than the angle of foveation. Within the angle of foveation, it is not possible to determine where someone is looking because all imagery falls on the high resolution part of the retina, called the fovea, and eye movement is unnecessary for visual interpretation.
However, despite the effectiveness of infrared bright-eye based eye tracking technology, the industry is highly motivated to abandon it and develop alternative approaches. This is deemed necessary because the infrared-based technology is not usable in environments with ambient sunlight, such as sunlit rooms, many public spaces, and the outdoors. To avoid raising concerns about potential eye damage, the amount of infrared radiation emitted by the illuminators is set to considerably less than that present in normal sunlight. This makes it difficult to identify the location of the bright eye and the primary reflection of the illuminator due to ambient IR reflections. This, in turn, diminishes the ability to compute the direction of eye gaze.